Web Inspector: don't report context ids before DidCommitLoad

Web Inspector: don't report context ids before DidCommitLoad
https://bugs.webkit.org/show_bug.cgi?id=89567

Reviewed by Pavel Feldman.

When inspector state is restored only report existing context ids
if "did commit load" even has already been dispatched.

* inspector/InspectorController.cpp:
(WebCore::InspectorController::InspectorController):
* inspector/PageRuntimeAgent.cpp:
(WebCore::PageRuntimeAgent::PageRuntimeAgent):
(WebCore::PageRuntimeAgent::restore):
* inspector/PageRuntimeAgent.h:
(WebCore):
(WebCore::PageRuntimeAgent::create):
(PageRuntimeAgent):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@120822 268f45cc-cd09-0410-ab3c-d52691b4dbfc